The present invention relates to fiber-optic communications networks, and more particularly, to optical network equipment such as optical amplifiers based on gain-clamped semiconductor optical amplifier devices with adjustable gain levels.
Fiber-optic networks are used to support voice and data communications. In optical networks that use wavelength division multiplexing, multiple wavelengths of light are used to support multiple communications channels in a signal band on a single fiber.
Optical amplifiers are used in fiber-optic networks to amplify optical signals. For example, optical amplifiers may be used to amplify optical data signals in the signal band that have been subject to attenuation over fiber-optic paths. A typical amplifier may include erbium-doped fiber coils that are pumped with diode lasers. Raman amplifiers and semiconductor optical amplifiers have also been investigated.
To reduce the effects of cross-talk, semiconductor optical amplifier devices may be gain clamped. With this type of arrangement, the waveguide portion of the semiconductor optical amplifier has a grating that creates feedback at a feedback wavelength that is outside of the signal band. The feedback grating extends along the entire length of the waveguide and induces lasing at the feedback wavelength. Because the semiconductor optical amplifier is lasing, the gain of the amplifier cannot exceed the loss of the amplifier at the lasing wavelength. This type of arrangement clamps the gain of the semiconductor optical amplifier at the laser wavelength and the wavelengths in the signal band.
With such gain clamped structures, the gain level cannot be varied. The grating may introduce large optical losses in the signal band, because the signals must traverse the gratings. In addition, the yields encountered when manufacturing such devices may be low, because it may be difficult to precisely achieve the desired gain level.
It is an object of the present invention to provide semiconductor optical amplifier arrangements with gain clamping and adjustable gain.
It is also an object of the present invention to provide optical network equipment such as optical amplifiers based on gain-clamped semiconductor optical amplifier devices that have adjustable gains.
These and other objects of the invention are accomplished in accordance with the present invention by providing gain-clamped semiconductor optical amplifier devices with adjustable gains and semiconductor optical amplifiers and other optical network equipment based on such semiconductor optical devices for use in handling optical data signals in a signal band in fiber-optic communications links. The fiber-optic communications links may carry a number of wavelength-division multiplexing channels each having a different corresponding wavelength. The equipment may use the semiconductor optical amplifier devices for providing optical gain for the optical signals:
Because the semiconductor optical amplifier devices are gain clamped, crosstalk between signals (i.e., between signals on different wavelength-division-multiplexing channels) is reduced. The ability to adjust the gain level of the devices may help to enhance the yield when manufacturing the devices. Optical amplifiers and other network equipment based on the gain-clamped semiconductor optical amplifier devices may be operated at different gain levels to accommodate installation of equipment of a given design in different network locations or to accommodate changing system requirements at a given equipment location.
Further features of the invention and its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.